Prior art helicopter supporting structures and framework comprises materials such as wood, aluminium, titanium, chrome molybdenum steel tubing and magnesium alloys. Fabrication and manufacturing of helicopter structures are based around the extensive use of special jigs and frames and certified holding fixtures where floors and jigs, frames and fixtures are frequently calibrated. Such installations have inherent disadvantages including that they are fixed in a location and are not mobile.
The prior art fuselage fabrication and manufacturing process requires the fuselage to be constructed by first assembling internal components and working outward. The prior art method of constructing a helicopter begins by identifying a starting location or part such as a central floor panel. The internal structure of the fuselage is then added systematically around that starting location by adding sub frames and panels. The assembly is then strengthened by riveting or bolting adjoining sub frames and panels to form a skeleton. Once all of the internal structure has been completed the fuselage skeleton is enclosed with a skin that is either riveted or bolted into place, usually by direct attachment to the skeleton. When the primary structure of the fuselage is completed and the fuselage is structurally sound it would be removed from the fabrication or manufacturing assembly jig.
Traditional helicopter fuselage manufacturing has numerous disadvantages. One disadvantage is that construction is extremely labour intensive. The completed fuselage has a vast number of individual parts, each requiring prior fabrication. To track and assemble these parts requires a skilled work force. Further, the fabrication jigs have long set-up times and long breakdown times. Production of helicopter fuselage in traditional manner is very expensive.
A further disadvantage to traditional helicopter manufacturing is the finished external surface of the helicopter fuselage covered in a mass of domed rivet heads. This type of finish is both unattractive and results in high drag penalties. Significant materials cost and time is associated with the use of flush head rivets in the outside skin of the fuselage to remove the drag penalty.
A further disadvantage to traditional helicopter fuselage fabrication using sheet metal panels to form the outer skin of the fuselage is the difficulty in achieving a smooth and thus aerodynamically favourable shape.
A further disadvantage to traditional helicopter fuselage fabrication is that door and window openings are typically hand finished. Finishing by hand results in no two door or window openings being the same. Each window or door therefore requires individual shaping, usually by hand, to ensure a fitment that allows closure without gaps.
A further disadvantage to traditional helicopter fuselage manufacturing using riveted structures and thus lapped joints is the ingress of moisture. This moisture becomes trapped and corrosion will ensue. Corrosion can lead to structural failure.
A prior art method of attaching empennage appendages to a fuselage is with a mechanical fastening such as rivets, screws or bolts. Mechanical fastenings such as riveted joints or bolted joints are known to be labour intensive and require the use of special fixtures and tooling jigs.
A disadvantage associated with use of mechanical fastenings to secure such appendages is that each of the adjoining surfaces must have a plurality of holes formed for the fastening to pass though. Such holes can cause weakening of the structure and may contribute to a point of structural failure. To mitigate the risk of structural failure such methods of fastening often require regular maintenance checks to ensure structural integrity is maintained, particularly for any cracks that may be propagating between adjacent holes.
Mechanical fastenings have a further disadvantage in that substantial damage may be caused to an aircraft by tearing the surrounding material should a secured appendage be struck by some external object.
Mechanical fastenings have a further disadvantage when attaching to curved surfaces together. The mismatch in shapes between the curved surface and the generally flat fastener may create undue stress on a location immediate to the fastener.
A further disadvantage is that mechanically fastened surfaces or riveted surfaces are prone to sealing issues where moisture can ingress or be trapped.
A further disadvantage is that mechanically fastened surfaces are prone to various types of corrosion. Filiform, intergranular and surface corrosion can form between mechanically fastened surfaces. Often, corrosion in these areas goes undetected even with periodic maintenance, dismantling and inspections and can result in catastrophic failure of the fastening or region proximate the fastening.
Traditionally helicopter crew and passenger seats have been inbuilt structures with the helicopter fuselage. Later years have seen crew and passenger seats evolve into stand-alone assemblies for the forward seats and foldaway seats for the rear passengers. Certification standards require the inclusion of a crashworthy seat for all occupants of the helicopter.
More recently since the introduction of new certification rules, seats in newly certified helicopters are required to be “Crashworthy” meeting certain design parameters of maximum load factors, inertial forces, and reactions between occupant, seat, and safety belt or harness corresponding with the applicable flight and ground load conditions, including the emergency landing conditions of the category in which certification is sought.
As a result there have been several newly design crashworthy seats installed into helicopters as new helicopter designs or retrofits to older helicopter designs. These new seat designs incorporate designs of shock absorber, collapsing lever mechanisms, brake, energy absorbing foams, and collapsible metal structures.
One seat design in the prior art for meeting the crashworthy seat standard is known as a stroking seat mechanism. Disadvantages of the stroking seat mechanism include the requirement for regular inspection and servicing, corrosion protection for metal surfaces, inadvertent jamming of the seat action and injuries to limbs that occur during the stroke of seat.
Another design in the prior art for meeting the crashworthy seat standard is known as a braking seat mechanism. Disadvantages of this seat mechanism include the friction pad loosing preload over time and the regular requirement for inspection and readjustment, the metal frame requires corrosion protection, inadvertent jamming of the seat action and injuries to limbs that occur during the stroke of seat.
Another design in the prior art for meeting the crashworthy seat standard is an aluminium sheet metal box design. Disadvantages of this seat mechanism include allowing the occupant to fall through the seat pan into the seat base. While the occupant may survive the crash, evidence has shown the occupant is subsequently trapped in the seat base and unable to escape the crashed aircraft.
In this specification, where reference has been made to external sources of information, including patent specifications and other documents, this is generally for the purpose of providing a context for discussing the features of the present invention. Unless stated otherwise, reference to such sources of information is not to be construed, in any jurisdiction, as an admission that such sources of information are prior art or form part of the common general knowledge in the art.
It is an object of the present invention to provide a solution which overcomes or at least ameliorates at least one of the abovementioned disadvantages or which at least provides the public with a useful choice.
Other objects of the invention may become apparent from the following description which is given by way of example only.